Dobby

ABSTRACT

A dobby mechanism provided with a lifting knife and link means connected to a heald frame. Means for interconnecting the lifting knife and link means including a latch. The lifting knife and latch being mounted to move in an arcuate path about a common axis. The apparatus includes means for selecting engagement of the latch with the lifting knife.

United States Patent Pavlica May 20, 1975 [541 DOBBY 2,705,505 4/1955 Staubii 1. 139568 2,751,938 6/1956 Staubiet alm... 139 68 [75] Invent: Zdenek f 11cm, 3,517,703 6/1970 Schwarz 139/68 Czechoslovak1a 73 Assignee: Elitex, Zavody teXlIlllllhO FOREIGN PATENTS B APPLICATIONS strojirenstvi generalni redielswi, 158,969 2/1921 Umted Kmgdom 139/74 Liberec Czechoslovakia 959,899 3/1957 Germany N................... 139/71 853,856 11/1960 United Kingdom 139/71 [22] Dem 1972 657,412 9 1951 United Kingdom 139/71 [21] Appl' 3l9307 Primary Examiner.lames Kee Chi Attorney, Agent, or Firm-Murray Schaffer [30] Foreign Application Priority Data Jan. 4, 1972 Czechoslovakia 3372-72 [57] ABSTRACT A dobby mechanism provided with a lifting knife and link means cmmected to a heald frame. Means for in [58] ne'ld 74 33' terconnecting the lifting knife and link means including a latch. The lifting knife and latch being mounted to move in an arcuate path about a common axis. The ludes means for selecting engagement of [56] References Cited apparatus 1 t h th th 1 k f UNITED STATES PATENTS c 6 m 2,635,644 4/1953 Staubli et al 139/68 11 Claims, 6 Drawmg F'gum PATENTEDMAYQU 191s SHEET 3 I]? 4 DOBBY BACKGROUND OF INVENTION The present invention relates to a dobby loom, Jacquard loom and the like and particularly to a loom having a double lift dobby intended to control the shedding operation.

In conventional looms the shedding operation is performed by the cooperative manipulation of the several harness heald frames and the hook cords. ConventionaIly this is accomplished by an arcuately moving lifting knife adapted to engage the hook cords and by a link means connected to the heald frame which includes a lifting crank having a latch selectively engageable with the lifting knife which causes the link means to operate. Convcntionally the lifting latch and lifting knife are mounted to move about independent axes and in separate paths relative to each other. This has presented a serious drawback to the construction of new and improved looms since it inhibits and generally prevents obtaining high speed operation, particularly in the raising and lowering of the heald shaft. This is a particular problem with new jet type looms in which the weft feed has been increased tremendously and which require a significant multiplication of the shedding changes as compared to conventional looms.

Still another drawback occurs in the prior art devices because of the different paths taken by the lifting latches and the lifting knife. During operation the engaging edges wear and readily deform because of the friction created in the two devices moving in separate paths. As a result frequent breakdown occurs and frequent costly changing of parts is required.

A further disadvantage is found in the prior art mechanisms for causing the latch to engage the lifting knife. This mechanism is generally controlled by a signal received from a memory storage or other machine control device, such as a patterning card, a magnetic tape or cord etc. The signal operates a servo mechanism which actuates the latch. Generally however, in large machines, the signal is often weak, the servo mechanism is out of time sequence or an excessively complex mechanism is required. These are costly, subject to breakdown and a constant nuisance.

It is the object of the present invention to provide a dobby mechanism, particularly of the double lift type which avoids the difficulty of the prior art devices.

It is a further object of the present invention to provide a dobby mechanism which is faster in operation and which can be used on high speed looms.

It is a further object of the present invention to provide a dobby mechanism which is simple, strong and long lasting.

These objects, others as well as numerous advantages will be seen from the following disclosure of the present invention.

SUMMARY OF INVENTION According to the present invention a dobby mechanism for the control of the shedding operation of a loom is provided comprising a lifting knife and link means for raising and lowering the heald shaft wherein the lifting knife and the latch means interconnecting it with the link means are mounted adjacent each other to move in arcuate paths the centers of which are coaxial. In addition, the dobby is provided with a mechanism for transmitting and amplifying the program signal and for positively actuating the latch when necessary to obtain conjoint movement.

Preferably, the lifting knife is supported on a carrier adapted to rotate about a fixed shaft, and includes means for oscillating the carrier in an are about the shaft being actuated by the dobby shaft. The latch is mounted at one end of a crank, also freely journalled about the shaft next to the carrier. The latch is provided with a hook, normally biased, out of engagement, with respect to the lifting knife, but movable by the signal transmitting and amplifying means into locking engagement with it when the program indicates. The engagement step is correlated to the dwell period in the movement of the lifting knife so that very little friction etc., occurs.

Still further in accordance with the present invention the signal transmitting and amplifying means comprises an impulse device arranged intermediate the programming means and the latch which acts directly on the latch in proper timing sequence and after the latch has reached its proper position thus insuring perfect time operation.

Full details of the present invention and its preferred embodiments are found in the following description and in the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS In the drawings:

FIG. 1 is a front elevation view of a single dobby unit according to the present invention,

FIG. 2 is a view of an impulse device for actuating the latch of the dobby,

FIG. 3 is a view of an alternate impulse device,

FIG. 4 is a schematic view of the reversible drive means for the impulse device,

FIG. 5 is a schematic view of the structure and operation of the lifting knives, and

FIG. 6 is a schematic view of the transmission linkage from the latch to the heald frame.

DESCRIPTION OF THE INVENTION The following description discloses the embodiment of the present invention in connection with the structure and form of a single double-lift dobby unit. It will be appreciated that a loom contains several healds or heddles in the harness which are basically identical, each being provided with the present invention. Furthermore, the following description omits reference to and details of a dobby loom, jacquard machine etc., which are well known and therefore would be only prolix if stated herein and cumbersome to the understand ing of the specific aspects of the present invention.

As seen in FIG. 1, the dobby mechanism comprises a pair of parallel shafts I and 2 about which are respectively mounted, for free rotation, double arm lifting cranks 3 and 4 which carry at the end of their upper arms double headed rocker latch members 5 and 6 each pivoted at their center. The latches 5 and 6 are provided, respectively with hooks 7 and 8 at one end and hooks 9 and 10 at the other end. Springs 11 and 12 bias the latches 5 and 6 counterand clockwise respectively.

The lifting cranks 3 and 4 are connected via an articulated linkage, comprising a tie rod 13, a balancing link 14, a connecting rod 15 and as seen in FIG. 6, via links l6, l7 and 18 to the associated heald frame 19 in the harness. Depending on which of the cranks 3 or 4 is moved the balancing link 14 pivots about pin 20 by which it is connected to lever 4 or pin 21 by which it is connected to rod 13. Further details of the linkage movement, the dimensions of the linkage and their function may be obtained from the inventors copending application, Ser. No. 319,308, now U.S. Pat. No. 3,833,027.

Mounted, also for free rotation, about the shafts 1 and 2 respectively, are carriers 101 and 102 to which the lifting knives 103 and 104 for the harness wire or cord hooks, conventional in such types of loom are secured. The knives 103 and 104 are connected together by a rod 105. The knife carrier 101 is bifurcated and provided with a pair of lower arms at the end of which cam follower rollers 106 and 107 are respectively mounted. The followers 106 and 107 engage opposing sides of the surface ofa combined positive and negative cam 108 which is fixed on the main shaft 109 of the dobby mechanism. Thus, as the dobby shaft 109 is rotated the carriers 10] and 102 are caused to swing and escillate in a reciprocating are about their respective pivot axis corresponding to shafts 1 and 2. Because of the connecting rod 105, the lifting knives 103 and 104 swing in unison. The carriers may, if desired, be separately driven and other means for their oscillation may be provided as is suitable.

Fixed stops 110 and 111 attached to opposite sides of the machine frame acts to limit the possible movement of the respective cranks 3 and 4 in their outward direction and constitute a position stop for the cranks at their dwell or rest position. Catches 112 and 113 are mounted adjacent the outward end of each of the respective latches and 6, each being adapted to engage and hold one of the hooks 9 and respectively, when the latches are normally biased by springs 11 and 12 secured between the outer end of the latch and the machine frame. The inner surfaces of the cranks 3 and 4 are provided with lands or stop surfaces 114 and 115 against which the edges of the respective lifting knives 103 and 104 are adapted to abut. lt is to be appreciated that the distances between the active edge of hooks 7 and 8 and their respective stops 114 and 115 are equal to the to the width of the associated lifting knives 103 and 104 so that the hooks may be made to engage and hold the knives.

Normally, the latches 5 and 6 are each biased by their springs 11 and 12 so that the respective hooks 9 and 10 engage the fixed catches 112 and 113. Thus, even though the dobby shaft 109 rotates and the carriers 10] and 102 oscillate the knives 103 and 104 about the respective pivot axes l and 2, the cranks 3 and 4 will not themselves swing. On the other hand should either of the latches 5 or 6 be moved against the bias of springs 11 or 12, then its hooks 7 or 8 would engage the associated lifting knife 103 or 104 and this engagement would cause the associated lever 3 or 4 to be driven by the appurtenant carrier 101 or 102 to swing conjointly with it resulting in the raising and lowering of the heald frame 19.

Along the center line between the latches 5 and 6 there are mounted a pair of spaced holders 116 and 117, from which depend flat blade springs 118 and 119 respectively, elongated and shaped to engage the top of the lifting knives.

The pivoting of the latches 5 and 6 is effected at the time in the system when it is desired, as will be obvious, to control the operation of the heald etc. The dobby or jacquard patterning machine is generally controlled by a patterning card, magnetic tape or memory card or similar device in which the specific fabric pattern is stored. From this memory an electrical or mechanical signal is obtained, in conventional manner, to operate the dobby mechanism.

The present invention provides an intermediate mechanism for transmitting and amplifying the signal from the memory unit in order to positively obtain actuation of the dobby mechanism. As seen in P16. 1 this latter mechanism, in one form, comprises an electromagnet or solenoid 201 whose armature 202 is connected to a perpendicularly arranged plunger 203 movably held in an annular bushing 204. The free end of the movable plunger 203 bears against the end of one arm of a pair of bell cranks 205 and 206 which are respectively mounted to pivot at their centers about pins 207 and 208. The bell cranks 205 and 206 are mounted in mirror image to each other with the ends beneath the plunger 203 located adjacent to each other so as to be simultaneously engaged by it. The number of bell cranks 205 and 206 corresponds directly to the number of latches 5 and 6. The outer or perpendicularly arranged arm of the bell cranks 205 and 206 are tubular and respectively carry a movable bolt 209 and 210 along an axis directed toward the upper surface of the latches 5 and 6. The bell crank levers 205 and 206 are biased counterand clockwise by springs 211 and 212 secured to the frame of the machine so that the adjacent opposed arms normally push the plunger 203 upwardly. Located below the opposed arms of bell cranks 205 and 206 are a pair of fixed members 213 and 214 secured to the machine frame which act as stops limiting the downward movement.

The signal thus received from the programming means does not act directly on the latch members, and therefore its strength is not critical. Furthermore, in this embodiment only a simple electromagnet is operated by the signal, which magnet merely acts to move the plunger, constituting the impulse means for actuating the latch, into proper position. Thus the function of position and impelling the bolt are separated. The bell crank lever requires little force to move it and therefore acts as an amplifier for the program signal.

Located above the upper ends of the bolts 209 and 210 respectively, are a pair of straight edge hammers or bars 300 and 301 which are movable into and out of abutment with the bolts to impel them downwardly. As seen in FIG. 4, the bars 300 and 301 are respectively secured to one end of substantially right angle brackets 302 and 303 which are pivoted about their centers on axles 304 and 305. Rollers 306 and 307 are secured at the other end of the respective brackets 302 and 303 and are adapted to ride against and follow the surface ofa rotatable control cam 308. It will be noted that the pivot axles 304 and 305 are spaced outside the bars 300 and 301 and in a position opposite to the corresponding bar which is mounted to it, and the roller followers 306 and 307 straddle the cam 308. Thus, the arrangement resembles a toggle or scissors construction. A spring 316 is connected at its ends to each of the arms of the brackets 302 and 303 straddling the cam so as to bias the follers against the cam surface.

The control cam 308 is provided with a central hole having a radial recess adjacent to it, in which a tooth 310 formed on a hub 311 extends. The hub 311 is keyed to a drive shaft 312 connected to the main shaft of the dobby. A spring load ball 313 is forced along a radial direction into a groove or hollow socket 314 formed on the circumferential surface of hub 311. In this manner the basic or normal position of cam 308 is determined by the ball and socket and the hub may be moved in either direction carrying the cam 308. On reverse motion of the dobby, the driving shaft 312 is reversed turning the hub 31 1, the cam 308 however, does not move at once since the clearance afforded by the recess 309 enables the hub 31] to move freely until the tooth 310 engages the opposite edge of the recess. Only after this engagement does the cam 308 move imparting subsequent movement to pivotal brackets 302 and 303. The cam circumference is formed with a radial projection 315 which is adapted to ride beneath the rollers 306 or 307 and lift the same, pivoting the brackets 302 and 303 accordingly.

This construction therefore, permits the cam 308 to actuate the bars 300 and 301 only after a sufficient time delay insuring that the lifting knife carrier and the lever supporting the latch are in stationary position or in dwell. relative to each other and that the impulse on the latch is made only during this dwell period. Thus, wear and deformation of the hooks is avoided. The mechanism described above operates as follows:

In response to the predefined weaving program recorded on the patterning card, magnetic tape or card memory or similar device, an electric impulse is emitted which is passed to the electromagnet 201 and by which it is energized. On energization the armature 202 is retracted moving the plunger 203 downwardly against the adjacent arms of cranks 205 and 206 simultaneously, swinging them from the normally biased position, (dotted lines FIG. 1), so that the free upper ends of each of the bolts 209 and 210 find themselves directly beneath the bars 300 and 301 respectively (see solid lines FIG. 1). Simultaneously the knives 103 and 104 are swung in abutment against the respective stops 114 and 115. Thereafter one of the bars 300 or 301 is activated by the cam 308 to strike the corresponding bolt 209 or 210 which moves downwardly against the upper surface of the associated latch 5 or 6 which is provided with a reinforced striker plate therefor. This lifts the corresponding hook 9 or 10 from engagement with its catch 112 or 113 and forces the inward end 7 or 8 onto and into fixed locked position on to the respective one of the lifting knives 103 or 104 (see dotted lines FIG. 1, showing the movement of latch 5 by the downwardly struck bolt 209). It is to be noted that in this condition both the lifting knife and latch are stationary relative to each other. The time period during which bolts 209 or 210 are intended to act on the associated latch is determined by the length of the cam projection 315 on the cam 308.

In the succeeding phase of operation the lifting knives 103 and 104 entrains the suspended hooked wires as well as carrying the cranks 3 or 4 with it. Once engaged by the lifting knife. the hooked wire is held securely thereto by the pressure of the flat spring 118. The appropriate crank 3 or 4 is carried by the lifting knife both of which are moved in an are about the common pivot axes 1 or 2, and the motion is transferred via the tie rod 13 and the balancing lever 14 to the heald frame 19.

After completing the rise of the lifting knife 103 the action of the knife carrier 10] or 102 causes the lifting crank 3 or 4 to swing backwardly with it since the carrier acts on the stop 114 or 115. As soon as the lever 3 or 4 is caused to abut the fixed stop or 111 thus placing the carrier and crank in dwell position and the associate bolts 209 and 210 are released from engagement with the upper surface of the respective latch, the spring 11 or 12 causes the latch to again open and then lock over the appropriate fixed catch 112 or 113.

It will be clear that the dobby acts symmetrically and corresponding in either direction of movement of the dobby shaft and that the actuation of either of the lifting knives and the combined movement with the cranks 3 0r 4 is the same. The only difference which exists for either one of the knives is that the pivot point about which the balance lever 14 turns is different. If crank 3 is moved the balance lever 14 pivots about pin 20. If crank 4 is moved the balance lever 14 pivots about pin 21. Greater detail of this movement will be found in the aforementioned copending application.

It will be noted that modification of cam 308 can be made to provide a contour surface in which both bars 300 and 301 can be simultaneous actuated and thereby impel both bolts 209 and 210 at the same time. entraining the cranks 3 and 4 on both knives.

The transmission of the signal from the program memory to the individual latches 5 and 6 can be obtained directly by a mechanical linkage in an embodiment shown in FIG. 2. Here a program may be stored on so called power card 400 comprising a drum 401 on the periphery of which are mounted a plurality of spaced pins 402 of unequal height. The drum 401 is mounted on a driving shaft 403 so that the pins 402 engage the inwardly directed arms of the crank levers 205 and 206. The longer pins 402 selectively move the levers 205 and 206 to pivot them, bringing the bolts 209 and 210 into line with the impulse bars 300 and 301, in the same manner as in the embodiment of FIG. 4.

The cards 400 or drums 401 can be used in still another arrangement as seen in FIG. 3. In this instance the pins 402 act directly upon a pair of elongated levers 215 and 216 which extend across each other being pivoted at their outer ends about the axles 207 and 208. The inner ends of the levers 215 and 216 bear directly on the oppositely situated latch 6 and 5 respectively which when moved by the pins 402 act in the manner described with either embodiment of FIG. 2 or FIG. 3. However, the extra impulse mechanism is not required.

It will be seen that the present invention removes the disadvantages inherent in the prior art and provides an improved dobby mechanism. Particularly, it will be seen that the latch action i.e., the placement of the hooks 7 or 8 over the associated lifting knife, takes place only during the dwell period of the dobby when both the lifting knife and the lifting crank are in relative stationary condition. Furthermore, during the actual period of time in which the heald frame is raised and lowered, the lifting knife and the lifting crank which it carries are conjointly moved in identical and contiguous arcuate paths, the centers of which are coaxial.

A further advantage is obvious from the use of the intermediate signal transmitting and amplifying means, in that complex scanning, electrical signal devices and mechanical actuators are not necessary. Only a small signal is required to move the latch bolts etc, into place so that the latch may close properly about the lifting knife. Also since the actual impulse to the latch is not dependent on the signal a strong sharp impulse, properly timed can be utilized to actuate the latch. This also permits the dobby to be reversed, as for example when searching for a mis-woven weft, without loss of synchronization or the need for resetting of the mechanism. It is necessary only to reestablish the impulse mechanism with respect to the dwell position of the dobby.

Various modifications, changes and alternations will be obvious to those skilled in this art. The disclosure is, therefore, intended to be illustrative and not limiting of the scope of the invention.

What is claimed:

1. A dobby for reversibly controlling the shed wires and the associated heald during the shedding operation of a loom comprising a pair oflifting knives, each lifting knife being respectively supported on a carrier, a pair of fixed shafts, each of said carriers being rotatably mounted on one of said shafts, means for oscillating each of said carriers in an arcuate path about its associated shaft, a crank associated with each lifting knife, said crank being mounted freely on the associated shaft to be rotatable about a common axis and in an arcuate path in proximity to its associated carrier, means connecting each crank to the associated heald, a latch pivotally mounted at its center at the end of each crank, said latch having a hook at one end engageable with the associated lifting knife when in proximity thereto, means for normally maintaining said latch out of engagement with the associated lifting knife, and means for selectively moving one or both of said latches to engage the associated lifting knife to cause said crank to move conjointly with said carrier thereby to move said heald simultaneously with one or both of said lifting knives.

2. The dobby according to claim 1 wherein the latch has a hook at its other end and the means for maintaining said latch out of engagement with said lifting knife comprises a stationary catch mounted adjacent the other end of said latch and spring means for biasing said other hook into engagement with said stationary catch.

3. The dobby according to claim 2, wherein the means for moving each of said latches comprises a lever adapted to pivot said latch to disengage the book from said stationary catch, said rod being moved by means responsive to signal received from a preprogrammed pattern.

4. The dobby according to claim 1 wherein one of said lifting knife carrier is provided with a pair of arms extending at an acute angle to each other, a rotating cam arranged between said arms, a cam follower roller secured to each of said arms and engaging the surface of said cam, and means connected to the main dobby drive to rotate said cam, said cam having a contour adapted to cause said arms to oscillate said carrier,

5. The dobby according to claim 3 wherein each of the levers for moving said latches comprise a bell crank, the arms of which being substantially perpendicular to each other, one arm of each bell crank extending toward the other, the other arm of said bell crank extending in a direction perpendicular to the associated latch, a movable bolt mounted on each of said other arms, means for driving each of said bolts into abutment with the corresponding latch, said drive eans being offset from the other arm, said cranks being movable to align said bolts with said drive means.

6. The dobby according to claim 5, including a plunger aligned with the arms of said bell cranks extending toward each other, said plunger being movable by means responsive to the signal from said preprogrammed pattern to move both said bell cranks simultaneously.

7. The dobby according to claim 6 wherein said plunger is actuated by an electromagnet.

8. The dobby according to claim 1 including resilient means mounted above said lifting knife adapted to engage the top of said lifting knife to secure the wire therein during movement of said lifting knife.

9. The dobby according to claim 5 wherein said drive means for each of the bolts respectively comprises a bar secured at the end of one arm of a right angle bracket pivotally mounted at its center, the other end of each of said brackets engaging a rotatable cam, said cam being driven to selectively to swing one or the other of said brackets.

10. The dobby according to claim 9 wherein said cam has a central hole having an offset recess, and the means for driving said cam comprises a shaft, a hub keyed to said shaft and entering said central hole, said hub having a radially extending tab entering said recess, said recess being larger than said tab, said shaft being drivable a predetermined time before said cam will rotate whereby a predetermined dwell interval is created before movement of said cam.

11. The dobby according to claim 1 including stops located on said lifting crank against which said lifting knives may abut, the distance between the hook engaging said lifting knives and said associated stop equalling the width of said lifting knife.

I: e a 

1. A dobby for reversibly controlling the shed wires and the associated heald during the shedding operation of a loom comprising a pair of lifting knives, each lifting knife being respectively supported on a carrier, a pair of fixed shafts, each of said carriers being rotatably mounted on one of said shafts, means for oscillating each of said carriers in an arcuate path about its associated shaft, a crank associated with each lifting knife, said crank being mounted freely on the associated shaft to be rotatable about a common axis and in an arcuate path in proximity to its associated carrier, means connecting each crank to the associated heald, a latch pivotally mounted at its center at the end of each crank, said latch having a hook at one end engageable with the associated lifting knife when in proximity thereto, means for normally maintaining said latch out of engagement with the associated lifting knife, and means for selectively moving one or both of said latches to engage the associated lifting knife to cause said crank to move conjointly with said carrier thereby to move said heald simultaneously with one or both of said lifting knives.
 2. The dobby according to claim 1 wherein the latch has a hook at its other end and the means for maintaining said latch out of engagement with said lifting knife comprises a stationary catch mounted adjacent the other end of said latch and spring means for biasing said other hook into engagement with said stationary catch.
 3. The dobby according to claim 2, wherein the means for moving each of said latches comprises a lever adapted to pivot said latch to disengage the hook from said stationary catch, said rod being moved by means responsive to signal received from a preprogrammed pattern.
 4. The dobby according to claim 1 wherein one of said lifting knife carrier is provided with a pair of arms extending at an acute angle to each other, a rotating cam arranged between said arms, a cam folloWer roller secured to each of said arms and engaging the surface of said cam, and means connected to the main dobby drive to rotate said cam, said cam having a contour adapted to cause said arms to oscillate said carrier.
 5. The dobby according to claim 3 wherein each of the levers for moving said latches comprise a bell crank, the arms of which being substantially perpendicular to each other, one arm of each bell crank extending toward the other, the other arm of said bell crank extending in a direction perpendicular to the associated latch, a movable bolt mounted on each of said other arms, means for driving each of said bolts into abutment with the corresponding latch, said drive means being offset from the other arm, said cranks being movable to align said bolts with said drive means.
 6. The dobby according to claim 5, including a plunger aligned with the arms of said bell cranks extending toward each other, said plunger being movable by means responsive to the signal from said preprogrammed pattern to move both said bell cranks simultaneously.
 7. The dobby according to claim 6 wherein said plunger is actuated by an electromagnet.
 8. The dobby according to claim 1 including resilient means mounted above said lifting knife adapted to engage the top of said lifting knife to secure the wire therein during movement of said lifting knife.
 9. The dobby according to claim 5 wherein said drive means for each of the bolts respectively comprises a bar secured at the end of one arm of a right angle bracket pivotally mounted at its center, the other end of each of said brackets engaging a rotatable cam, said cam being driven to selectively to swing one or the other of said brackets.
 10. The dobby according to claim 9 wherein said cam has a central hole having an offset recess, and the means for driving said cam comprises a shaft, a hub keyed to said shaft and entering said central hole, said hub having a radially extending tab entering said recess, said recess being larger than said tab, said shaft being drivable a predetermined time before said cam will rotate whereby a predetermined dwell interval is created before movement of said cam.
 11. The dobby according to claim 1 including stops located on said lifting crank against which said lifting knives may abut, the distance between the hook engaging said lifting knives and said associated stop equalling the width of said lifting knife. 